Hi @lylewiescamp
Here's an ifixit article that may help.
https://www.ifixit.com/News/69041/how-batteries-can-catch-fire-and-how-to-prevent-it
Scroll towards the end of the article to see what you can do.
If the Chromebook is still working the best option is to leave it turned on (without the charger connected) until it shuts down.
It won't be completely discharged as the battery management chip will prevent this from happening but it's the best that you can do.
Here's a teardown [https://www.youtube.com/watch?v=E-YdsA32Oh0|video] that may help to gain access to the battery etc.
Don't forget to responsibly dispose of the battery afterwards. ;-)